Microwave paleointensities from dyke chilled margins: a way to obtain long-term variations in geodynamo intensity for the last three billion years

Halls, H. C.; McArdle, Nick; Gratton, M. N.; Hill, Mimi J.; Shaw, John

doi:10.1016/j.pepi.2004.03.013

Cited by 25 publications

(20 citation statements)

References 20 publications

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“…Macouin et al (2006) together with results from this study. The summarized data are from Morimoto et al (1997), Yoshihara & Hamano (2000, , Sumita et al (2001), Yu & Dunlop (2001, 2002; Smirov et al (2003), Macouin et al (2003), Halls et al (2004), Macouin et al (2006), McArde et al (2004), Thomas & Piper (1995) and Biggin et al (2009). Closed star indicates result from this study and open circles represent secondary magnetization.…”

Section: Palaeointensitymentioning

confidence: 76%

Palaeomagnetism and geochronology of the Proterozoic dolerite dyke from southwest Greenland: indication of low palaeointensity

Miki

Taniguchi

Yokoyama

et al. 2009

Geophysical Journal International

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S U M M A R YIntensity of the geomagnetic field during the Archaean can potentially be used to study an evolution of the dynamo activity in the Earth's core. In order to investigate this issue, we present new palaeomagnetic and geochronological results from the dolerite dyke, which have been intruded into the Archaean Gneisses of Nuuk area, southwest Greenland. 40 Ar/ 39 Ar dating of the pyroxene grains from dolerite yield an age of 2585 ± 21 Ma. The high temperature component, which has been recognized as a characteristic direction, is identified in 24 dolerite samples. Comparison of the palaeomagnetic directions from dolerite dykes with those from host gneisses suggests a primary origin for this component. Magnetic mineralogical and grain size investigations revealed a pseudo-single domain magnetite as a dominant career of magnetization. Thellier palaeointensity determinations of 14 dolerite specimens yield a mean field value of 13.9 ± 2.5 μT. Strength of the virtual dipole moment (2.30 ± 0.42 × 10 22 Am 2 ) obtained from this study is about one quarter of the present Earth's filed value. A simulation based numerical model of the Thellier experiments suggests that the presence of multidomain grains can play a role in enhancing the strength of palaeointensity. Even after taking in to account the effects of multidomain grains, an intensity value (13.9 μT) from this study suggests that the strength of geomagnetic field at about 2.6 Ga was much lower than that of the present time.

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Section: Palaeointensitymentioning

confidence: 76%

Palaeomagnetism and geochronology of the Proterozoic dolerite dyke from southwest Greenland: indication of low palaeointensity

Miki

Taniguchi

Yokoyama

et al. 2009

Geophysical Journal International

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“…Halls et al (2004) suggested that the difference between their results and those of Macouin et al (2003) may be due to the presence of secondary magnetizations in the samples used in the earlier study.…”

Section: Comparison With the Early Paleoproterozoic-neoarchean Paleoimentioning

confidence: 77%

“…Stars indicate the sites that yielded three or more successful paleointensity determinations (Table 1) (e.g., Halls, 2008). Several dike swarms have been successfully used for paleointensity determinations (e.g., Macouin et al, 2003Macouin et al, , 2006Smirnov et al, 2003;Halls et al, 2004;Shcherbakova et al, 2008).…”

Section: Figmentioning

confidence: 99%

“…Fifteen successful Thellier anal- Muxworthy et al (2013) Notes: * Corrected for the cooling rate, anisotropy of remanent magnetization, and non-linear TRM acquisition; * * corrected for magnetomineralogical alteration during laboratory experiments; * * * corrected for the cooling rate. Halls et al (2004) used the microwave-Thellier technique (e.g., Walton, 1991;Walton et al, 1996) The Neoarchean data also include two Thellier paleointensity determinations based on slowly cooled rocks. Selkin et al (2008) obtained a mean VDM of 5.05 ± 1.46 × 10 22 A m 2 from 53 sites of the ∼ 2.7 Ga Stillwater Complex (Montana, USA) after correcting their data for the cooling rate, remanence anisotropy, and nonlinear TRM acquisition.…”

Section: Comparison With the Early Paleoproterozoic-neoarchean Paleoimentioning

confidence: 99%

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Geomagnetic paleointensity at ∼2.41 Ga as recorded by the Widgiemooltha Dike Swarm, Western Australia

Смирнов

Evans

2015

Earth and Planetary Science Letters

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“…Casas et al, 2005) to geological (e.g. Hill et al, 2002b;Thomas et al, 2004;Halls et al, 2004;Gratton et al, 2005b;Hill et al, 2005).…”

Section: Microwave Palaeointensity Systemsmentioning

confidence: 99%

The use of the ‘Kono perpendicular applied field method’ in microwave palaeointensity experiments

Hill

Shaw

2007

Earth Planet Sp

Self Cite

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For a complete understanding of the Earth's magnetic field behaviour it is necessary to have information regarding variations in its strength as well as directional changes. In order to reduce the lengthy experimental time for palaeointensity experiments and potentially reduce the possibility of mineralogical alteration Kono suggested a single heating perpendicular applied field variant of the most widely used double heating palaeointensity method (the Thellier method). Whilst in the past this method has not been generally used, due mainly to technical difficulties, it is ideal for use with the microwave palaeointensity technique. Reproducing the amount of microwave energy absorbed by a sample is not as simple as reproducing the temperature in an oven so a palaeointensity method that only has a single application of microwave power at each step is an advantage. One of the uncertainties in the original Kono method lies in getting the natural remanent magnetisation of the sample aligned perpendicular to the applied laboratory field. With the microwave systems this uncertainty has been essentially removed. The microwave variant of the perpendicular applied field method which incorporates checks for perpendicularity, as well as the usual checks for alteration and non ideal behaviour is routinely applied as it is quick and easy to use, avoids any potential power reproducibility issues and provides a comparison with results obtained through other methods.

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Microwave paleointensities from dyke chilled margins: a way to obtain long-term variations in geodynamo intensity for the last three billion years

Cited by 25 publications

References 20 publications

Palaeomagnetism and geochronology of the Proterozoic dolerite dyke from southwest Greenland: indication of low palaeointensity

Palaeomagnetism and geochronology of the Proterozoic dolerite dyke from southwest Greenland: indication of low palaeointensity

Geomagnetic paleointensity at ∼2.41 Ga as recorded by the Widgiemooltha Dike Swarm, Western Australia

The use of the ‘Kono perpendicular applied field method’ in microwave palaeointensity experiments

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